In conventional optical devices, a spherical wave radiated from a point light source located at a focus of a lens can be converted into a plane wave after being refracted by the lens. A lens antenna consists of a lens and a radiation source disposed at the focus of the lens. By means of the convergence property of the lens, an electromagnetic wave radiated from the radiation source is converged by the lens before being transmitted outwards. Such an antenna has a high directionality.
Currently, the convergence property of the lens is achieved through a refraction effect of the spherical shape of the lens. As shown in FIG. 1, a spherical wave radiated from a radiation source 30 is converged by a spherical lens 40 and then transmitted outwards in the form of a plane wave. The inventor has found in the process of making this invention that, the lens antenna has at least the following technical problems: the spherical lens 40 is bulky and heavy, which is unfavorable for miniaturization; performances of the spherical lens 40 rely heavily on the shape thereof, and directional propagation from the antenna can be achieved only when the spherical lens 40 has a precise shape; and one antenna can only operate at a single operating frequency and cannot make a response to frequencies other than the operating frequency.